Hi The +12 goes straight to the OCXO. All OCXO’s have a voltage sensitivity. That sensitivity is much higher than voltage sensitivity is much higher than what you see on the other two supply pins.
Bob > On Oct 21, 2016, at 11:06 PM, Scott Stobbe <[email protected]> wrote: > > Interesting, I would have thought that the +12V input would be extremely > well regulated since its shared with the oven heater, I*R drops are going > to show up every where, if your looking for uV levels of stability. > Just a connector has milliohms of contact resistance, let alone routing and > cables... > > On Friday, 21 October 2016, Bob Camp <[email protected]> wrote: > >> Hi >> >>> On Oct 21, 2016, at 7:44 PM, Scott Stobbe <[email protected] >> <javascript:;>> wrote: >>> >>> A little more data on the 7912. >>> >>> The first plot shows the tempCo of the 7912 measured with ambient >>> temperature swings "7912_TempCo.png". Which is -150 ppm/degC. >>> >>> The second plot is off a 7912 logged for an hour or so, "7912_1PLC.png", >>> nothing too interesting here. However the environmental temperature swing >>> of about 1 degC/hour is pretty conservative for a DUT sitting in free >> air. >>> >>> Finally, an allan devation plot looking at the normalized stability of a >>> 7912 regulator "7912_AllanDeviation.png". Interestingly here, is, how >> quick >>> a 15 mK/min temperature swing shoots above the 1/f floor, it's a matter >> of >>> seconds. >>> >>> Now if your PSRR is 1 ppb/V or better, then all of this is comfortably >>> below the intrinsic noise of a thunderbolt. >> >> The main point is that the internal tempco of the TBolt it’s self is much >> larger than >> the issues surrounding the power supply pins. The +12 is the only one that >> is >> sensitive enough to voltage (change in frequency vs voltage) to contribute >> to any >> significant way to the overall stability. >> >> Bob >> >>> >>> On Fri, Oct 21, 2016 at 12:20 AM, Scott Stobbe <[email protected] >> <javascript:;>> >>> wrote: >>> >>>> Nick had mention that the -12V rail on the thunderbolt has the poorest >>>> PSRR with respect to frequency output, so I first took a look at the >>>> venerable 7912. >>>> >>>> The first data-set was taken with a -13.5 VDC input. Attached is the 0.1 >>>> Hz to 10 Hz noise of an essentially quiescently loaded 7912, only a 10k >>>> resistor was added as load for preliminary evaluation. With a 60 dB >> preamp >>>> the scale of the scope plot is 20 uV/div. The 0.1Hz to 10Hz band noise >> is >>>> 15 uVrms, which is about 1.3 ppm rms of the DC mean. >>>> >>>> In allan deviation terms, a quiescently loaded 7912 has a spot noise of >> 7 >>>> uV/rtHz at 1 Hz (on the 1/f slope), normalized that's 580 ppb/rtHz. >>>> Equivalently speaking, the flicker noise floor of an allan deviation >> plot >>>> would be sqrt(2*ln(2)) that figure to be 6.8E-7. >>>> >>>> Assuming a thunderbolt should be achieving 1/f floor of around 1E-12, it >>>> would need a PSRR of at least 1 ppm/V. I'm sure someone has gone to the >>>> trouble of actually measuring it. >>>> >>>> So from a 0.1 Hz to 10 Hz noise standpoint, the 7912 isn't terrible >>>> with 1.3 ppm rms noise, considering an LM399 is about 0.1 ppm rms, only >> one >>>> order of magnitude off. >>>> >>>> The bad side of a 7912 is in long-term stability and tempCo, the sample >> I >>>> tested had at least a 150 ppm/degC tempCo, which is going to put a >> serious >>>> lump/bump in the 10s tau to gps crossover point on an allan deviation >> plot. >>>> >>>> >>>> >>>> On Tue, Oct 18, 2016 at 3:05 PM, Scott Stobbe <[email protected] >> <javascript:;>> >>>> wrote: >>>> >>>>> I'm sure I have some 7805s lying around, maybe a 7812/7912. I'm >>>>> interested to see the 1/f noise of a classic regulator, what load >> current >>>>> do you expect? I can bias a 7805 for the same load and measure the 0.1 >> to >>>>> 10 Hz noise. >>>>> >>>>> Also if you have a digital scope without a very good builtin FFT, >> octave >>>>> would be one solution. >>>>> >>>>> On Tue, Oct 18, 2016 at 10:46 AM, Nick Sayer via time-nuts < >>>>> [email protected] <javascript:;>> wrote: >>>>> >>>>>> Just an update. I’ve built the second prototype board (I skipped over >>>>>> the first design), and it’s powering my tbolt right now. >>>>>> >>>>>> The design calls for 15v in (though it would also work with 13.8v). >> The >>>>>> +12 output comes from a D2PAK 7812. For +5, there is an AP1509 buck >>>>>> converter to make around 6.5 volts, then a DPAK 7805. For -12, there >> is an >>>>>> MC34063 configured as an inverter to make around -13.75 volts and >> then a >>>>>> DPAK 7912. >>>>>> >>>>>> Steady-state, the system appears to be working just fine. The AP1509’s >>>>>> inductor and the D2PAK 7812 are just warm to the touch. >>>>>> >>>>>> I checked for noise and ripple on the outputs and it’s somewhere >> around >>>>>> ±2 mV or so generally. From what I can see on the scope, there’s no >> ripple >>>>>> - it’s all high frequency noise. I am not absolutely certain that the >> noise >>>>>> measurement represents real noise or the limits of my measuring >> ability. >>>>>> I’m just using the scope probes the scope came with, and 2 mV/div is >> its >>>>>> lowest range. >>>>>> >>>>>> I haven’t compared the noise with the ex laptop supply that I was >> using >>>>>> before, but I’d have to believe it’s cleaner. I don’t really have a >> way to >>>>>> check the oscillator’s before and after ADEV. My only other reference >> is an >>>>>> FE5680A, and I think the thunderbolt’s going to be far better at >> lower tau >>>>>> (where this all matters). >>>>>> >>>>>> I know also that ±2 mV is still one and perhaps two orders of >> magnitude >>>>>> higher than some have called for. But before I attempt to reduce the >> noise >>>>>> further, I’d like to know that there are real gains to be had. Would >>>>>> someone with a Thunderbolt and better output noise measuring >> wherewithal be >>>>>> willing to take a prototype and compare it with something that does >> have µV >>>>>> levels of noise and ripple so I can get an idea of what there is to >> gain? >>>>>> If you like, you can make such comparisons public - no secrets here. >>>>>> >>>>>>> On Aug 30, 2016, at 10:37 PM, Nick Sayer <[email protected] >> <javascript:;>> wrote: >>>>>>> >>>>>>> >>>>>>>> On Aug 30, 2016, at 8:48 PM, Cube Central <[email protected] >> <javascript:;>> >>>>>> wrote: >>>>>>>> >>>>>>>> I would be interested, I think. Planning ahead for if the one I >> have >>>>>> for my Thunderbolt fails, I guess. Are there different models or >> would a >>>>>> photo of the input ports on mine be useful? >>>>>>> >>>>>>> Actually, what I had in mind is to just put a SIP4 header on the >> board >>>>>> for the output and people could wire the “last mile” themselves. The >> input >>>>>> is a 2.1mm barrel connector. You use whatever 15W 12VDC wall wart is >> handy >>>>>> and plug it right in. >>>>>>> >>>>>>> What it really amounts to is that you get +12 volts directly from the >>>>>> input, then there’s a buck converter to drop the +12 down to +5 and an >>>>>> inverter to generate -12 from the +12. Those 3 voltages, plus a >> ground go >>>>>> to the SIP4. >>>>>>> >>>>>>> So it’s just two switching power supplies to turn a +12 volt only >>>>>> supply into the three-way that the Thunderbolt wants. >>>>>>> >>>>>>> It’d be good for around 1500 mA @ 5V and around 50 mA @ -12 (the +12 >>>>>> spec is whatever is left from the source supply’s power spec) - more >> than >>>>>> enough for a Thunderbolt. Probably enough for a hard disk or a >> smallish PC. >>>>>> _______________________________________________ >>>>>> time-nuts mailing list -- [email protected] <javascript:;> >>>>>> To unsubscribe, go to https://www.febo.com/cgi-bin/m >>>>>> ailman/listinfo/time-nuts >>>>>> and follow the instructions there. >>>>>> >>>>> >>>>> >>>> >>> <7912_1PLC.png><7912_AllanDeviation.png><7912_ >> TempCo.png>_______________________________________________ >>> time-nuts mailing list -- [email protected] <javascript:;> >>> To unsubscribe, go to https://www.febo.com/cgi-bin/ >> mailman/listinfo/time-nuts >>> and follow the instructions there. >> >> _______________________________________________ >> time-nuts mailing list -- [email protected] <javascript:;> >> To unsubscribe, go to https://www.febo.com/cgi-bin/ >> mailman/listinfo/time-nuts >> and follow the instructions there. >> > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
